YieldStar uDBO Overlay Metrology in Samsung D1y DRAM Volume Production

To produce high-yielding wafers, overlay control in DRAM production needs to be exceptionally tight. The ASML YieldStar 375F introduces a continuous wavelength source and dual wavelength operation to deliver the high measurement accuracy and robustness required as input to the overlay control loop. At the same time, the high throughput required to allow high sampling densities is maintained. The YieldStar 375 was evaluated and adopted for Samsung's D1y DRAM node. The evaluation was performed in 3 phases: 1. In the setup phase, recipe optimization was done using YieldStar's Holistic Metrology Qualification approach. 2. Following recipe setup, the overlay performance for all layers was compared to TOR in the shadow monitoring phase, using both single and dual WL recipes. 3. During the on-product evaluation phase, Samsung was running latest flexible wavelength YieldStar model in control for critical FEOL layers as a final step for HVM adoption. The on-product evaluation confirmed the shadow monitoring outcome and showed performance consistent with recipe qualification results. Moreover, both machine-to-machine matching and throughput were well within Samsung's expectation for both single and dual wavelength recipes. As a result, Samsung decided to adopt YieldStar 375F as the tool of record (TOR) for overlay correction in volume production on critical front end of line (FEOL) layers. Following the change to overlay corrections by Yieldstar 375, the rework rate on several critical layers decreased by more than 1 percentage point.